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BIOLOGY YEAR 1 > Biological Molecules > Flashcards

Biological Molecules Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What are monomers?

A

The smaller repeating subunits from which larger molecules are made.

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2
Q

What are polymers?

A

Molecules made from a large number of monomers joined together.

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3
Q

How is a condensation reaction work?

A

A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water.

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4
Q

What is a hydrolysis reaction?

A

A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule.

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5
Q

What are monosaccharides?

A

The monomers from which larger carbohydrates (which always contain C, H and 0) are made.

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6
Q

Examples of common monosaccharides…

A

Glucose, galactose and fructose.

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7
Q

What does a condensation reaction between two monosaccharides form?

A

A glycosidic bond (in the disaccharide)

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8
Q

How is maltose formed?

A

The condensation of two glucose molecules.

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9
Q

How is sucrose formed?

A

The condensation of a glucose molecule and a fructose molecule.

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10
Q

How is lactose formed?

A

The condensation of a glucose molecule and a galactose molecule.

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11
Q

What are isomers?

A

Molecules with an identical molecular formula but distinct arrangements of atoms in space.

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12
Q

What are the structures of the two isomers of glucose?

A

Alpha glucose: OH below
Beta glucose: OH above
ABBA

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13
Q

How is cellulose formed?

A

The condensation of beta glucose.

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14
Q

How are polysaccharides formed?

A

The condensation of many glucose units.

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15
Q

How are glycogen and starch formed?

A

The condensation of alpha glucose.

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16
Q

Describe the structure of one component of starch.

A

Amylose (20%) is a long, unbranched chain of a-glucose. The angles of the glycosidic bonds give it a coiled structure, and hydrogen bonds between a-glucose molecules hold this in place.

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17
Q

Describe the structure of the other component of starch.

A

Amylopectin (80%) is a long, branched chain of a-glucose.

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18
Q

How do properties of starch support its function?

A
  • Coiled so it is compact so its good for storage as you can fit more into a small space.
    -Insoluble so does not affect water potential.
    -Large molecule so cannot leave the cell- good for storage and contains lots of glucose units.
    -Amylopectin has side branches which allow the enzymes to hydrolyse the glycosidic bonds easily, releasing a-glucose quickly.
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19
Q

Describe the structure of cellulose.

A

Made of long, unbranched chains of b-glucose, where every other b-glucose is inverted. When b-glucose molecules bond, they form straight cellulose chains which are linked together by hydrogen bonds to form strong fibres called microfibrils.

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20
Q

How do properties of cellulose support its function?

A

The strong fibres (microfibrils) mean cellulose provides structural support for cells (e.g. in the plant cell walls).
Can resist turgor pressure/osmotic pressure.
Resists digestion/action of microorganisms.

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21
Q

How do properties of glycogen support its function (as an energy store)?

A

-Coiled so its compact, good for storage.
-Insoluble so does not affect water potential.
-Loads of branches means that stored glucose can be released quickly-important for energy release in animals which have a higher respiration rate and therefore metabolic rate than plants.

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22
Q

Describe the structure of glycogen.

A

Very similar to amylopectin, except that it has loads more side branches coming off it.

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23
Q

Plants store excess glucose as starch…

A

…Animals store excess glucose as glycogen.

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24
Q

Describe the biochemical test for reducing sugars.

A

-Add Benedict’s reagent to a sample.
-Heat in a water bath that’s been brought to the boil.
-Positive result: coloured precipitate: green-> yellow-> orange->brick red- reducing sugar present.

The higher the concentration of reducing sugar, the further the colour change goes. An accurate way of measuring this would be to filter the solution and weigh the precipitate or use a colorimeter.

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25
Q

What are reducing sugars?

A

Reducing sugars can donate electrons to reduce another molecule. This includes all monosaccharides and some disaccharides- maltose and lactose

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26
Q

Describe the biochemical test for non-reducing sugars.

A

If result of reducing sugars test is negative…
-Add dilute hydrochloric acid to a new sample and heat in a water bath that has been brought to the boil.
-Neutralise it by adding sodium hydrogencarbonate.
-Carry out Benedict’s test as normal.

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27
Q

Describe the biochemical test for starch.

A

-Add iodine dissolved in potassium iodide solution to sample.
-Positive result: colour change from brown-orange to blue-black.

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28
Q

What are lipids made from?

A

They are NOT POLYMERS, but are instead made from a variety of different components, and they all contain hydrocarbons.

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29
Q

Two groups of lipids.

A

Triglycerides and phospholipids.

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30
Q

How are triglycerides formed?

A

The condensation of 1 molecule of glycerol and 3 molecules of fatty acid. This forms an ester bond between glycerol and a fatty acid (RCOOH).

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31
Q

How does the structure of triglycerides relate to its function?

A

Long hydrocarbon tails of fatty acids contains lots of chemical energy- when oxidised they release about twice as much energy as carbohydrates of the same mass.
Low mass: energy ratio- more energy can be stored in small volume (reduces the mass that animals need to carry e.g. camels)
Insoluble in water- do not affect the water potential and therefore osmosis.
High ratio of H:O atoms- when oxidised they release water-important source for animals.
Triglycerides bundle together as insoluble droplets in cells because fatty acid tails are hydrophobic-the tails face inwards, shielding themselves from water with their glycerol heads- waterproof, waxy cuticles in plants.

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32
Q

What properties of lipids makes them insoluble in water?

A

Fatty acid molecules have long ‘tails’ made of hydrocarbons. The tails are ‘hydrophobic’ meaning they repel water molecules.

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33
Q

Describe the difference between saturated and unsaturated fatty acids.

A

The difference is in their hydrocarbon tails (R groups). Saturated- contains single carbon to carbon bonds only, the fatty acid is ‘saturated’ with hydrogen.
Unsaturated- carbons linked by one or more double bonds.

34
Q

How to carbon to carbon double bonds affect the structure and properties of fatty acids?

A

Double bonds causes the chain to kink, so it cannot pack closely together. They have a lower melting point and are found as liquids at room temperature e.g. oils. But fats are generally made of saturated fatty acids and are solid at room temperature.

35
Q

What are the lipids found in cell membranes and how are they different to triglycerides?

A

Phospholipids have a similar structure to triglycerides except one of the fatty acid molecules is replaced by a phosphate group. The phosphate group is hydrophilic (attracts water) whilst the fatty acid tails are hydrophobic (repel water).

36
Q

How is the structure of phospholipids related to its properties?

A

Phospholipids make up the bilayer of cell membranes, which control what enters and leaves the cell. Phospholipid heads are hydrophilic and their tails are hydrophobic so they form a double layer with their heads facing out towards the water on either side. The centre of the bilayer is hydrophobic, so water-soluble substances can’t easily pass through it- the membrane acts as a barrier to those substances.

37
Q

Describe the biochemical test for lipids.

A

-Add ethanol to sample and shake solution and then add water.
-A white emulsion is a positive result.

38
Q

What are the monomers of proteins?

A

Amino acids. The twenty amino acids that are common in all organisms differ only in their R group.

39
Q

How are dipeptides and polypeptides formed?

A

A condensation reaction between two amino acids forms a peptide bond.
Dipeptides are formed by the condensation of two amino acids.
Polypeptides are formed by the condensation of many amino acids.

40
Q

What is the role of DNA?

A

DNA holds genetic information.

41
Q

What is the role of RNA?

A

RNA transfers genetic information from DNA to the ribosomes.

42
Q

What are ribosomes formed from?

A

RNA and proteins.

43
Q

Describe the structure of a nucleotide.

A

A pentose (Deoxyribose in DNA, Ribose in RNA), a phosphate group and a nitrogen-containing organic base (Adenine, Cytosine, Guanine or Thymine in DNA, Uracil in RNA).

44
Q

What does a condensation reaction between two nucleotides form?

A

A phosphodiester bond between the pentose sugar and the phosphate group (and one molecule of water)

45
Q

Describe the structure of a DNA molecule.

A

A double helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs. The chain of phosphate and sugars is known as the sugar-phosphate backbone.

46
Q

What are the differences in structure between DNA and RNA?

A

DNA is double stranded, RNA is single stranded.
DNA has Thymine, RNA has Uracil.
DNA is long, RNA is short.
RNA is less stable than DNA- doesn’t have two sugar-phosphate groups.
DNA has deoxyribose, RNA has ribose

47
Q

Describe the difference between purines and pyrimidines.

A

A and G are double-ring structures : Purines.
C and T are single-ring structures: Pyrimidines.

48
Q

Describe the process of DNA replication, which takes place in the nucleus.

A

DNA helicase breaks hydrogen bonds between polynucleotide strands/base pairs, unwinding DNA.
Both strands act as a template.
Free nucleotides bind to the template strands.
Complementary base pairing occurs (A-T, C-G).
DNA polymerase joins nucleotides on the new strand forming phosphodiester bonds in a condensation reaction.
Replication is semi-conservative, because the new DNA molecule contains one original and one new strand. This means that there is genetic continuity between generations of cells.

49
Q

Why can nucleotides only be added in a 5’ to 3’ direction?

A

-DNA has antiparallel strands.
-Shape of the nucleotides at the 5’ end is different to the 3’ end.
-DNA polymerase is an enzyme with a specific active site.
-It is only complementary to the 3’ end.
-This is why replication occurs in opposite directions on the two strands.

50
Q

Explain how the structure of DNA supports its function.

A

-Tightly coiled around histone proteins, making it compact so full genome can fit into every cell.
-Being a long molecule allows it to store a lot of genetic information.
-Individually weak hydrogen bonds allows chains to be unwound for replication/transcription.
-Lots of hydrogen bonds between complementary base pairs gives the molecule stability and provides strength.
-Complementary base pairing enables transcription/replication.
-Sugar-phosphate backbone provides strength, ensuring DNA is a stable information carrier.
-Sequence of bases allows genetic code to be stored.

51
Q

How can very different organisms have a very similar percentage of each base in their DNA?

A

-Different genes
-Triplets in different sequence
-Different amino acid/protein coded for

52
Q

How is DNA in a prokaryotic cell different to DNA in a eukaryotic cell?

A

-Circular in prokaryotic, linear in eukaryotic
-A does not equal T and C does not equal G therefore there is no base-pairing so DNA is not double-stranded in prokaryotic cells.

52
Q

What has the relative simplicity of DNA led many scientists to doubt before 1953?

A

That it carried the genetic code.

53
Q

What did Watson and Crick do?

A

By 1953 experiments had shown that DNA was the carrier of the genetic code, and this was also the year that the double helix structure was determined by scientists Watson and Crick.
Watson and Crick also came up with the theory of semi-conservative replication.

54
Q

What was there uncertainty about before Watson and Crick’s theory was proved in Meselson and Stahl’s experiment?

A

Whether replication was conservative or semi-conservative. If it was conservative, the original DNA strands would stay together and the the new DNA molecules would contain two new strands.

55
Q

Describe Meselson and Stahl’s experiment. (Stage 1)

A

The experiment used two isotopes of nitrogen (DNA contains nitrogen), heavy nitrogen (with a mass of 15), and light nitrogen (with a mass of 14).
-Two samples of bacteria (E.coli) grown for many generations- one in a nutrient broth containing light nitrogen, and one in a broth with heavy nitrogen. As bacteria reproduced, they took up nitrogen from the broth to help make nucleotides for new DNA, so the nitrogen gradually became part of the bacteria’s DNA.
-A sample of DNA was taken from each batch of bacteria, and spun in a centrifuge. The DNA from heavy nitrogen bacteria settled lower down the centrifuge tube than the DNA from the light nitrogen bacteria.

56
Q

Describe Meselson and Stahl’s experiment. (Stage 2)

A

-The bacteria grown in heavy nitrogen broth were taken out and put in a broth containing only light nitrogen, and left for one round of replication, then another DNA sample was taken out and spun in a centrifuge.
-The DNA settled out between where the light nitrogen DNA settled out and where the heavy nitrogen DNA settled out, so replication was semi-conservative.

57
Q

What would the results have looked like if replication was conservative?

A

The original heavy DNA, which would still be together, would settle at the bottom and the new light DNA would settle at the top.

58
Q

What is a single molecule of ATP formed from?

A

A single molecule of Adenosine Triphosphate is a nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and 3 phosphate groups.

59
Q

Why is ATP essential for plant and animal cells?

A

Plant and animal cells release energy from glucose- respiration. A cell can’t get its energy directly from glucose. So, in respiration the energy released from glucose is used to make ATP. It then diffuses to the part of the cell that needs energy.

60
Q

How is the energy stored in ATP?

A

In high energy bonds between the phosphate groups.

61
Q

What does the hydrolysis of ATP produce?

A

ATP is broken down into ADP (Adenosine Diphosphate) and an inorganic phosphate. A phosphate bond is broken and energy is released, and the reaction is catalysed by the enzyme ATP hydrolase.

62
Q

What is the hydrolysis of ATP used for?

A

Energy used to:
-enable more muscle contraction
-make bonds- DNA replication, protein synthesis
-active transport, cell division
-enzyme action
-condensation and hydrolysis reactions

The hydrolysis of ATP can be coupled to energy-requiring reactions within cells.

63
Q

Explain the concept of phosphorylation.

A

The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive.

64
Q

How can ATP be resynthesised?

A

In a condensation reaction between ADP and an inorganic phosphate. This happens during both respiration and photosynthesis and is catalysed by the enzyme ATP synthase.

65
Q

Why is ATP useful in many biological processes?

A

-Releases energy in small amounts- little danger of thermal death of cells.
-Broken down in one step/single bond broken.
-Energy available rapidly/immediate energy source.
-Phosphorylates, making substances more reactive, lowering their activation energy.
-Reformed.

66
Q

Explain why it is necessary to synthesise such a large amount of ATP?

A

-ATP is unstable.
-It cannot be stored/is an immediate energy source.
-Active transport/named process using ATP

67
Q

Why is water a polar molecule?

A

Water has a partial negative charge on one side and a partial positive charge on the other. This is because oxygen has a greater affinity for electrons than the hydrogens so it ‘pulls’ the electrons closer. This makes oxygen slightly negative and the hydrogens slightly positive, so they form hydrogen bonds.

68
Q

Explain the importance of water in organisms.

A

-A metabolite in many metabolic reactions, including condensation and hydrolysis reactions.
-An important solvent in which metabolic reactions can occur-important substances can be dissolved and transported around the body.
-Relatively high heat capacity, buffering changes in temperature-makes a stable environment for aquatic organisms.
-Relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation.
-Strong cohesion between water molecules; supports columns of water in tube-like transport cells of plants (e.g. xylem) and provides surface tension where water meets air- pond skaters.

69
Q

What properties of water are important in the cytoplasm of cells?

A

-Polar molecule- acts as solvent.
-Solvent- metabolic reactions occur faster in solution.
-Reactive- takes place in hydrolysis reactions.

70
Q

Where do inorganic ions occur?

A

In solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations.

71
Q

Describe the role of hydrogen ions.

A

The concentration of hydrogen ions in a solution determines the pH, which is important for enzyme-controlled reactions.

72
Q

Describe the role of iron ions.

A

A key component of haemoglobin in red blood cells that is made of 4 polypeptide chains that each contain 1 iron ion. Haemoglobin binds to oxygen and transports it around the body.

73
Q

Describe the role of sodium ions.

A

The co-transport of glucose and amino acids across cell-surface membranes (e.g. in small intestine).

74
Q

Describe the role of phosphate ions.

A

Attaches to other molecules to form phosphate groups- essential component of DNA, RNA and ATP.
In ATP bonds between phosphate groups store energy.
Found in phospholipids- phospholipid bilayer of cell membranes.
Phosphorylation of other compounds making them more reactive.

75
Q

How can a colorimeter be used to determine the unknown concentration of a substance?

A

Use a colorimeter to measure the absorbance of a series of known concentrations to create a calibration curve. Compare the absorbance of an unknown sample to the calibration curve, interpolate to find out it’s concentration.

76
Q

How can we make the Benedict’s test quantitative?

A

A quantitative Benedict’s test produces a colour whose intensity depends on the concentration of reducing sugar in a solution. A colorimeter measures the intensity of this colour.

77
Q

Describe how a calibration curve was made to determine the concentration of an unknown sample of reducing sugar.

A

-Make a dilution series: make glucose solutions or different, known concentrations.
-Carry out quantitative Benedict’s test on each sample and the unknown sample (add Benedict’s solution and heat).
-Using a colorimeter, measure the absorbance value of each solution.
-Plot a calibration curve
-Find the concentration of unknown sample from graph through interpolation.

78
Q

Describe how a calibration curve was made to determine the concentration of an unknown sample of reducing sugar.

A

-Make a dilution series: make glucose solutions or different, known concentrations.
-Carry out quantitative Benedict’s test on each sample and the unknown sample (add Benedict’s solution and heat).
-Using a colorimeter, measure the absorbance value of each solution.
-Plot a calibration curve
-Find the concentration of unknown sample from graph through interpolation.

79
Q

What equation can be used to make dilutions?

A

C1 × V1= C2 × V2

80
Q

How do you use a colorimeter?

A

-Put the colorimeter on Absorbance (to measure the absorbance in nm) Select the green filter (520nm)
-Fill a cuvette with distilled water (this is your ‘standard’) to calibrate the colorimeter (this will also be your reading for 0% concentration) Press ‘R’ (to reference the colorimeter on the distilled water)
-Remove the cuvette containing distilled water
-Place your sample in the colorimeter
-Press ‘T’

BIOLOGY YEAR 1 (4 decks)

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